Many structures in the United States, and in particular commercial structures, have single-glazed windows. These windows were installed when costs of heating were low and before fuel shortages had made clear the need to conserve energy resources. In contrast, buildings now being constructed generally have double- or even triple-glazed windows. As a further measure to conserve energy, venetian blinds are sometimes employed in association with such windows. Window units having two or more glazings with a venetian blind located between the glazings are currently available for installation in new buildings or for refitting buildings having less energy efficient windows. The venetian blind structure serves both to decrease the loss of radiant energy through a window from a warm building in cold weather and to reduce the radiant energy entering a cool building in hot weather.
The cost of replacing inadequate single-glazed windows in an existing building is considerable. The old windows must be removed, frames repaired or replaced, and new windows installed. The process disrupts the use of the rooms in which the windows are located, leaves the building open to the weather for a period of time, and may even require cordoning off sidewalks or other areas beneath the windows in order to prevent the chance of injury to passersby from falling materials. As a consequence of all of these disadvantages, as well as the considerable expense of entirely new replacement windows, many inadequate single-glazed windows remain unimproved, adding to the energy problem of the country.
The prior art is generally cognizant of double-glazed windows having a window blind or sunscreen located between the glazings. For typical examples, see McCarthy, U.S. Pat. No. 2,849,762, and Requena, U.S. Pat. No. 3,324,620. Examples of the use of adjustable blinds of the venetian blind sort interposed between exterior and interior glazings are seen in Pratt, U.S. Pat. No. 2,631,339, Cummings, U.S. Pat. No. 3,022,549, Klopstad, U.S. Pat. No. 3,128,823, and Toth, U.S. Pat. No. 3,443,624. Sometimes provision is made for the entire, double-glazed window with the enclosed window blind to open, the window typically being hinged at one side, as in Pratt, or pivotted about some selected axis of the window, as in Toth.
The advantages of the structures shown in the prior art, either expressly discussed in the prior art or understood by implication, are the advantages offered by double-glazing in reducing thermal conduction through a window, and by enclosing a shade between panes of glass. The shade provides a substantial screening coefficient which greatly reduces solar radiation through the window while selectively permitting such radiation when additional interior heat is desired. The enclosed shade cannot be bumped or otherwise disturbed in normal use and will not collect dust. The double-glazed windows with blinds shown in the prior art are designed to be made and installed as complete units, to be used either in new construction or to entirely replace a conventional window when used in refitting an existing structure.
Debs, U.S. Pat. No. 3,703,920, shows a venetian blind adapted to be installed in a commercial double-glazed window of a particular metal frame construction that includes a framing channel along one edge of the space between the window panes, wherein the space is sufficiently wide to accommodate the shade. Thus, the double-glazed window construction is altered to include the energy saving benefits of the venetian blind.
The prior art windows make no provision for upgrading a previously installed, conventional single-glazed window so as to provide both an additional sealed window and, in combination therewith, a venetian blind mounted on the sash of the additional window and within the air space between the old and new window panes. Instead, when it has been necessary to upgrade existing structures to include energy efficient double-glazed windows with enclosed blinds, conventional structures and methods require removal of existing windows and replacement with entire new double-glazed units with enclosed venetian blinds. As a consequence, refitting an existing building with energy efficient windows typically requires extensive remodeling, expensive window and blind components, and considerable expense.